The present invention relates to cellular foamed materials, and more particularly to a three-dimensionally reinforced cellular matrix composite material characterized by lightweight and high impact resistance properties.
The use of high-performance composite fiber materials is becoming increasingly common in applications such as aerospace and aircraft structural components. As is known to those familiar with the art, fiber reinforced composites consist of a reinforcing fiber such as carbon or KEVLAR(copyright) and a surrounding matrix of epoxy resin, PEEK or the like. Most of the well-known composite materials are formed by laminating several layers of textile fabric, by filament winding or by cross laying of tapes of continuous filament fibers. However, all of the laminated structures tend to suffer from a tendency toward delamination. Thus, efforts have been made to develop three-dimensional braided, woven and knitted preforms as a solution to the delamination problems inherent in laminated composite structures. Representative three-dimensional textile preforms are disclosed in U.S. Pat. No. 5,465,760 issued to Mohamed et al. on Nov. 14, 1995 and U.S. Pat. No. 5,085,252 issued to Mohamed et al. on Feb. 4,1992.
Also, it is well-known to make conventional foamed materials, such as foamed polymer plastic materials, that have microcellular voids distributed throughout the material. Standard techniques for this purpose normally use chemical or physical blowing agents. For example, chemical blowing agents are low molecular weight organic compounds which decompose at a critical temperature and release a gas or gases such as nitrogen, carbon dioxide, or carbon monoxide. Methods using physical agents include the introduction of a gas as a component of a polymer charge or the introduction of gases under pressure into molten polymer. These well-known and standard foaming processes produce voids or cells within the plastic materials which are relatively large (for example, on the order of 100 microns or greater), as well as relatively wide ranges of void fraction percentages, for example from 20% to 90% of the parent material. The number of voids per unit volume is relatively low and often there is a generally non-uniform distribution of the cells throughout the foam material such that the materials tend to have relatively low mechanical strengths and toughness. See, for example, U.S. Pat. No. 3,796,779 issued to Greenberg on Mar. 12, 1976.
It is also well-known in the foamed materials art that in order to improve the mechanical properties of conventional cellular foam materials, a microcellular process was developed for manufacturing foam plastics having greater cell densities and smaller cell sizes. See, for example, U.S. Pat. No. 4,473,665 issued on Sep. 25,1984 to J. E. Martini-Vredrensky et al. The improved technique provides for pre-saturating the plastic material to be processed with a uniform concentration of a gas under pressure and the provision of a sudden induction of thermo-dynamic instability in order to nucleate a large number of cells. For example, the material can be pre-saturated with the gas and maintained under pressure at its glass transition temperature, and the material then suddenly exposed to a low pressure to nucleate cells and promote cell growth to a desired size, depending on the desired final density, and thereby producing a foamed material having microcellular voids or cells therein. The material is then quickly further cooled, or quenched, to maintain the microcellular structure.
Additional work in producing microcellular foam plastic material is described in U.S. Pat. No. 4,761,256 issued on Aug. 2, 1988 to Hardenbrook et al. Further, U.S. Pat. No. 5,334,356 and U.S. Pat. No. 5,158,986 both issued to Baldwin et al. disclose apparatus and process for forming a supermicrocellular foamed material having cells distributed throughout the material with average cell sizes being at least less than 2.0 microns and preferably in a range from about 0.1 micron to about 1.0 micron.
Although all of the above is well-known to those skilled in the textile arts and microcellular foamed material arts, applicants have recognized the need for an improved three-dimensional composite material which does not tend to delaminate and that possesses lightweight and very high impact resistance. Toward that end, applicants have developed a new three-dimensionally reinforced cellular matrix composite and the method for making the product that allows for the formation of three-dimensional reinforced composites with a cellular matrix that contains intentionally induced voids. The voids render the composite material extremely light in weight while simultaneously providing enhanced impact resistance and enhanced specific bending stiffness. Applicants believe that this novel composite material is new in the composite art and meets a long-felt need for such a product and a method for making the product.
Summarily, applicants have discovered a novel three-dimensionally reinforced cellular matrix composite and a method for making the same that combines cellular technology with three-dimensional textile preform technology in order to provide a novel lightweight composite material with superior structural integrity.
In accordance with the present invention, applicants provide a lightweight and impact resistant composite material comprising a three-dimensional textile structure preform formed of at least three systems of yarns that define a plurality of interstices within the textile structure. A cellular matrix material fills the interstices of the three-dimensional textile structures and coats at least a portion of the surface area of the three-dimensional textile structure.
In accordance with another aspect of the present invention, applicants provide a method of producing a three-dimensionally reinforced cellular matrix composite including providing a three-dimensional textile structure preform formed of at least three systems of yarns that define a plurality of interstices within the textile structure. Next, a foamable polymer material is introduced to the three-dimensional textile structure preform so as to fill the interstices and impregnate the three-dimensional textile structure preform and to coat at least a portion of the surface area of the structure. The foamable polymer material is then foamed to produce a microcellular foamed polymer material containing a plurality of voids or cells distributed substantially throughout the foamable polymer material.
It is therefore an object of the present invention to provide a three-dimensionally reinforced cellular matrix composite that is lightweight and impact resistant.
It is another object of the present invention to provide a three-dimensionally reinforced cellular matrix composite that incorporates a three-dimensional textile structure preform in order to provide enhanced structural integrity.
It is another object of the present invention to provide a three-dimensionally reinforced cellular matrix composite that incorporates a three-dimensional textile structure preform to provide enhanced performance characteristics including enhanced resistance to delamination.
It is still another object of the present invention to provide a three-dimensionally reinforced cellular matrix composite that incorporates a three-dimensional textile structure preform and that provides enhanced resistance to delamination, enhanced impact resistance, enhanced fatigue life, enhanced strength-to-weight ratio, and enhanced stiffness-to-weight ratio.
Some of the objects of the invention having been stated, other objects will become apparent with reference to the drawings described hereinbelow.